Electrical measuring instrument



July-12, 1938. E; F. WESTON I 2,123,670

ELECTRICAL MEASUR ING INSTRUMENT Filed Aug. 16, 1935 2 Sheets-Sheet l July 12, 1938. E. F. wEsToN 2,123,670

ELECTRICAL MEASURING INSTRUMENT Filed Aug. 16, 1935 2 Sheets-Sheet 2 Patented July l2, i938 r4turen TATEs f PATENT ortica Weston Electrical Instrument Corporation,

Newark, N. J., a corporation of Nev.1 .lersey Application August 16 1li Claims.

This invention relates to electrical measuring instruments and particularly to light metersfor the measurement or indication Oflight intensity.

Meters of this type include a photocell of the barrier layer type and a sensitive measuring instrument, the instrument being Agraduated in erms of foot candles and/or in block ranges of light values. Jlt has-beenfproposecl 'to locate the photocell and the instrument side by side in 'a 3o single elongated casing and, according to anotherdesign, the photocell was used as the scale plate of the 'instrlnnent 'K An object of. this invention is to provide an electrical measuring instrument of novel physical l5 design-which maybe manufactured as a relatively small unit. An object is to provide a light meter in-whch the photocell is positioned adjacent and parallel to the instrument scale plate.

A further object is to provide a light meter in which the photocell and scale plate form a single assembly" that may be readily mounted upon and electrically connected to the associated measuring instrument elements. A further object is to provide a measuring instrument in which the v scale plate constitutes a guide and support for the cover glass of the instrument, the scale plate4 and cover glass being-retained in pla/.caba casing which encloses the instrument'and is secured to the instrument base. Other objects are to provide measuring instruments having parts of novel design that simplify and facilitate the assembly of the instrument. v These and other objects and advantages of the invention will be apparent from the following 35 specification when taken with the accompanying drawings in which:-

Fig. l is an enlarged front elevation of one embodiment of the invention;

Fig. 2 is a longitudinal central section through the same;

Fig. 3 is a transverse section'on the plane of line 3-3 of Fig. 5;

Fig. 4 is a perspective view of the clamp which secures all of the `instrument parts to the base; Fig. 5 is an elevation, with parts broken away, of the light meter as seen with the casing removed;

Fig. 6 is a fragmentary section on line 6--6 of 50 ng. 5;

- Fig. '7 is a perspective view of the core and coil mounting bracket;

Fig. 8 is a perspective view of the core and its mount; 'l A Fig. 9 is a perspective view'of the insulating 1935, Serial No. 3659i (ci. iss-23) plate which carries the 'scale plate and cell, a portion of the cell being also shown;

Fig. l0 is a perspective view of the scale plate;

stamping since, as will be explained later, the

base may serveas a part of the circuit of the light meter.

The circular magnet 3 rests upon bosses il and 5, 5 which rise above the base to support the central section and the ends, respectively, ofthe magnet. 'The bent ends 6 of Wide U-clamp 'l extend over the magnet and a bolt B is passed through the center of the clamp to secure the magnet to the base.- Shifting of the magnet is prevented/by4V extending the bracket bolts 9 into holes/in the bosses 5, the nuts it on the bolts /having a fairly snug fit with the holes. The core and coil supporting bracket ll! is a thin ymetal stamping having outer ears l2 that are apertured to receive the bolts S, and upper and ,lower flanges i3, it, respectively, which 'have alined openings for receiving the usual jewels or bearings l5 of the movlngcoil lli. The central portion of the bracket has a rectangular opening ll for receiving one edge of the brass lug or strip i8 which has its opposite edge secured in a slot in the magnetic core lil. The strip i8 extends through the bracket and is staked over, as shown at 20, Fig. 2, to secure the core to the bracket. Attention is directed to the fact that, for clearness of illustration, Figs. 7 and 8 are not to scale.

The bracket for a small instrument may be stamped from sheet brass of a thickness of, for example, about 0.05 inch, and the brass lug or core mounting I8 may be sheet brass of about 0.06 inch thick. The bends of the bracket Il are preferably strengthened by indentations 2 l.

The circuit connections to the coil i6 'are made, in the usual way, throughv the coil springs 22, 23. The lower spring is insulated from the bracket ll and base 2, while the upper spring 23 is grounded on the bracket. The coil I6 carries a pointer 24 which moves over scale indications that, preferably, are a series of blocks 25a, 25h, etc., which correspond to ranges of light values. The several blocks are of different contrasting orange, yellow, green, blue.

colors and legends may be placed adjacent the blocks to indicate the character of work for which the'measured light value is'appropriate. As indicated by the cross-hatching of the scale blocks in Fig. 1, the colors may be arranged in the following order, as viewed from left to right: red,

The instrument has a high sensitivity for low light values where the eye strain is critical and maybe rea Vwith sffi cient accuracy in bright light where the question of eye strain is less critical when thelight values for theY several block ranges correspond to, for example, to l0, 10 to 20, 20 to 50, 50 to 100 and. 100 to 250 candles per square foot, respectively.

The scale blocks are painted or printed on a etallic, referabmbrassrscaleiplate 2S, Fig.

vof the plate adjacent the upper corners and the opening 32 are extended as lugsv 33, 36 which pass through notches 33', 34' in the edge of, and are bent under a mounting plate of insulating material Sii, Fig. 9.

The photocell 2l is looselyA mounted in a rectangular opening in the mounting plate, and its outer electrode surface is held in engagement with its upper terminal, i. e., the metal scale 777777 plate 26, by a lower spring terminal 37, Fig. ll,

which'is secured to the mounting plate 35 by the bent ends of integral lugs 33. The spring terminal has reinforcing ribs 39 and spring fingers d that are bent upwardly Vtowards the photocell.

lThe yoke extensionsillwof the mounting plate are apertured to nt snugly'over the upper extensions 9 of the bracket bolts 9, and screws i2 are threaded into the extensions 9' to secure fr the mounting plate 35 to the magnet and base.

yand the magnet 3.

The opposite edge of the mounting plate has an opening :3 tting over a pin extension dit on a boss d5 which supports the upper edge of the plate, and the clamp i has upturned lugs 6', Fig. 4, which bear against and support the loweri edge of the mounting plate.

rihe electrical circuit connections between the cell and the coil it are made, in part, by the engagement of the bent lugs 3d of the scale plate with bosses d6, Fig. 6, of the metallic base 2. The upper spring 23 of the coil system is also grounded upon the base 2 by the bracket ii The circuit is completed by the lead il which is soldered to the lower spring 22 and to a terminal lug 33 on the spring terminal plate 3l.

With this electrical connection completed, the glass cover plate Si is placed upon the flanges 29 of the scale plate 2d, and the casing i is slipped over the assembly and secured to the base 2 by two screws fit. i'l'.lhe scale plate is a thin sheet or plate and the flaring edges provide a spring support for holding the glass cover against the casing.

The electrical and mechanical assembly of the instrument are exceedingly simple but the parts are all rmly retained in proper relation through the bolts 9 that secure` the coil and core bracket to the magnet. The lower ends of the bolts enof the measuring instrument.

giaceva gage the base to prevent a shifting of the magnet 3 that is secured to the base by the single clamp l; The bolts also support and prevent shifting or' the mounting plate 35 which carries the scale plate and cell assembly.

The cell 2l is closely adjacent the plane of f the scale plate and is below the pointer 2d but the shadow cast upon the cell does not apprecblme f e readings, particularly when the meter is graduated, a s mung@ of light values. it is to be understood that the mw' measuring instrument is of relatively high sensitivity to provide indications of substantial magnitude from a barrier layer type of photocell of smaller size than the instrument scale plate. The light meter shown in the drawings has operated satisfactorily with an active cell area of less than one square inch.

It is 'to be understood that the invention is not restricted to the particular construction 2@ herein illustrated and described as many changes which may be made in the size, shape and relationship of the various parts fall within the scope of my invention as set forth in the following claims. I claim:

1. Ina light meter, an electrical measuring instrument including a casing, a magnet within said casing, a coil .pivotally mounted in thfield of said magnet, a thin metal scale plate within said casing a pointer carried by said coil and movable over said scale plate, a photoelectric cell within said casing, means including a con-l ductive terminal member in contact with one face of said cell for securing said scale plate and cell to each other in parallel closely adjacent positions, and conductive means including said terminal member and said scale plate electrically connecting ysaid cell to said coil.

- 2. A light meter as claimed in claim l, wherein said scale plate is prtured, and `s`aid"eil "y behind the scale plate.

3. In a light meter, the combination with the casing, magnet and moving coil system of a measuring instrument, of an insulatingmount- A5 ing plate having an opening therein, a photocell within said opening, means supporting said mounting piatein said casing in xed position with respect to saicaghet, and terminal plate members for said cell secured to and supported by said mounting plate at the opposite sides thereof.

4. A light meter as claimed in clairn 3, wherein the terminal plate member at the outer side of said mounting plate comprises the scale plate 5. In a light meter, a cell assembly adapted tc be mounted in the casing of a measuring instrument, said assembly comprising a mounting plate of insulating material having means for sef curing the same within the instrument casing, said plate `having an opening therethrough, a photocell in said opening, an apertured terminal plate at 'one side of said mounting plate and having portions thereof extending over the said cell, and a terminal plate of spring material at the opposite side of said mounting plate for holding the cell against the said portions of the apertured terminal plate.

6. In a light meter, an electrical measuring lnstrument having a casing, a magnet, a moving coil, a bracket secured to said magnet and supporting said coil, a scale plate, a pointer carried by said coil for movement over said scale plate,

a photoelectric 'cell of the nat disk current= gg generating type, a mounting plate of insulating material and means for securing the same in ilxed position within said casing, said plate having an opening in which said cell is located, means securing said scale plate to said mounting plate, terminal members secured to said moving coil, and means including said bolts for supporting said cell .from said base.

8. A light meter as claimed in claim 7, wherein said means securing said magnet to said base includes a clamp fastened to said base and overlying said magnet, and said bolts extend into recesses in said base to prevent sluiting movement of the magnet with respect to said base.

9. In a light meter, an electrical measuring instrument comprising a base, a magnet and moving coil carried by said base, a pointer mounted on said coil, a scale plate supported from said base in position to cooperate with said pointer, said scale plate having edge portions -forming a seat for a cover glass, a cover glass on said seat, a photoelectric cell connected across said coil, means including said scale plate for supporting said cell, a casing for said instrument, and means securing said casing to said base.

l0. A light meter as claimed in claim 9, wherein said scale plate is metallic and forms one terminal connection to said cell.

11. In a light meter, the invention as claimed in claim 9, wherein said scale plate is resilient and presses said cover glass against thel inner side -of said casing when said casing is secured to said base.

12. A photoelectric measuring instrument comprising a base, a magnet and means securing the same'to said base, a coil and core in the field o! said magnet, a bracket supporting said coil and core, an indicating system including a pointer carried by said coil and a scale plate, a photoelectric cell 'and means securing the same to said scale plate, and means for supporting said scale plate and cell from said magnet. y v

i3. A measuring instrument as claimed in claim 12, wherein said scale plate is apertured, and said cell is positioned behind said scale plate to receive light through the aperture thereof.

14. In a measuring instrument, a base, a magnet and moving coil supported on said base, a scale plate, a pointer carried by said coil and movable over said scale plate, a. mounting plate of insulating material, said scale plate being metallic and having lugs locking the same to the mounting plate, a photoelectric cell carried by said mounting plate, a spring terminal plate secured to said mounting plate and pressing said cell into contact with said scale plate, and means including said scale plate and terminal plate connecting said cell across said coil.

EDWARD F. WESTON. 

